Interface advance control in pattern floods by retarding cusp formation



JUY 23 1968 D. L.. HOY-r r-:TAL 3,393,734

' I INTERFACE ADVANCE CONTROL IN PATTERN FLOODS BY RETARDING CUSP FORMATION Filed Dec. 28, 1965 United States Patent O M INTERFACE ADVANCE CONTROL IN PATTERN FLOODS BY RETARDING CUSP FORMATION Donald L. Hoyt and Anthony F. Altamira, Houston, Tex.,

assignors to Texaco Inc., New York, N.Y., a corporation of Delaware Filed Dec. 28, 1965, Ser. No. 516,891 10 Claims. (Cl. 166-9) ABSTRACT OF THE DISCLOSURE A method of improving the areal sweep efficiency across a pattern of wells penetrating a subterranean hydrocarbon-bearing formation wherein the formation of a cusp at the corner well is retarded by controlling the advance ofthe flow gradients via production at the adjacent wells.

This invention relates generally to the production of hydrocarbons from underground hydrocarbon-bearing formations, and more particularly, to a method for increasing the overall production of hydrocarbons therefrom.

In exploiting underground hydrocarbon-bearing formations through a plurality of wells, it has been the general practice that when a production well yields an excessive amount of an extraneous fluid other lthan the hydrocarbons, e.g., water or gas, that production Well is shutin and t-he production of hydrocarbons is started and carried out at other production wells in the field. It is known that in such instances, a substantial amount of hydrocarbons is left behind in the 'hydrocarbon-bearing formation since such is not considered primarily recoverable economically.

Secondary recovery programs are now -an essential part'of the over-all planning for virtually every oil and gas-condensate reservoir in underground hydrocarbonbearing formations. In general, this involves injecting a fluid into the reservoir zone to drive the oil or gas toward producing wells by the process frequently referred to as flooding Usually, this flooding is accomplished -by drilling wells in a geometric pattern, the most common pattern being the 5-,spot.

When fluid from the injection well reaches the producing wells in a 5-spot pattern, the areal sweep efficiency is about 71%. By continuing production well past breakthrough, it is possible to produce much of the remaining unswept portion. It would be a great economic lbenefit to be Aable to achieve a sweep efficiency of 100% of the hydrocarbon-bearing formation. It would be an even greater benefit to be able to achieve it at breakthrough, so that it would not be necessary to produce large quantities of' injected fluid.

Accordingly, it is an object of the present invention Yto provide an improved method for the production and recovery of hydrocarbons, particularly liquid petroleum, from underground hydrocarbon-bearing formations,

Another object of this invention is to provide a method whereby t-he areal sweep efficiency in pattern flooding is improved.

These and other objects, advantages and features of this invention will become apparent from a consideration of the specification with reference to the figures of the accompanying drawings wherein:

FIG. 1 discloses four units of an inverted 5spot pattern;

FIG. la is illustrative of the interface advance in the form of a cusp toward va corner producing well in one quadrant of such al 5-spot pattern undergoing secondary recovery;

3,393,734 Patented July 23, 1968 FIG. 2 discloses one unit of a quadrilateral side well pattern of 13 wells;

FIGS. 2a and 2b illustrate the movement of the interface during the phases of productioin programs inpone quadrant of such a quadrilateral side well pattern undergoing secondary recovery; and

FIG. 3 kdiscloses a special case of a quadrilateral side well pattern of 13 wells having four additional interior production wells.

In our concurrently filed, coassigned application for patent for Interface Advance Control in Pattern Floods by Use of Control Wells, there is disclosed how an increased amount of hydrocarbons is produced and recovered from an underground hydrocarbon-'bearing formation by employing at least three wells, penetrating such a formation, which wells can be in-line, to produce hydrocarbons from the formation via two of these wells including the middle well, as disclosed in the co-assigned U.S. Patent No. 3,109,487, issued to Donal-d L. Hoyt, on Nov. 5, 1963.

It is understood that the failure of the driving flood in secondary recovery operations to contact or sweep all the hydrocarbon area is due to the development, in the interface, of a cusp which advances toward the production well. If other portions of the interface could be made to keep up, or if the cusp formation were delayed, complete areal sweep would be possible. In the cited coassigned application, a production control well is positioned between the injection well and the production well and is kept on production even after the injection fluid reaches it. In this manner, the cusp is pinned down at the control well and while the area swept out by the injection fluid before breakthrough at the last production well is increased, there is an unwanted handling of considerable quantities of injection fluid at the control well.

Another aspect to increase the sweepout eflciency is disclosed herein and involves the retardation of the development of the cusp toward the production well. The method of achieving more uniform advance is to control the flow gradients so that the interface is spread out. This can be done either by choosing a particular geometry of Well positions or by adjusting the relative production rate so that the velocity of advance is not predominantly in one direction. It can be done also by shifting the gradients frequently, in both direction andmagnitude, thus preventing any one section of an interface from advancing too far out of line.

The figures of the drawings schematically disclose and illustrate the practice and the advantages of our invention with well patterns and areal sweep-out examples which are obtainable and have been observed both in secondary recovery operations an-d in potentiometric model studies which simulate secondary recovery operations. The model studies indicate a sweep-out obtained in an ideal reservoir, although the recovery from an actual sweep-out of a particular field may be greater or less, depending on field parameters. The results to be described were based the following set of experimental conditions and assumptions:

(1) The ratio of total fluid production rates between wells is constant for any given phase or step in the production plan for all units in a pattern (a pattern unit is the basic group of an injection well with surrounding production wells, the repetition of which makes up the overall pattern of the production field);

(2) All the units in any pattern produce at the same rate (this requires that Wells at the edge of the field produce at 1A or 1/2 of the rate of corresponding interior wells, depending on whether they are corner or side wells, respectively, in a pattern unit);

(3) The total fluid injection and production mu'st balance for each patern unit, as well as for the Whole pattern;

(4) The mobility ratio of the displacing to the displaced fluid is 1.0;

In the special case of the l7spot pattern of FIG. 3, production can be maintained (a) at all wells till breakthrough at the interior production wells; (b) then with these wells shut in, further production is maintained at Gravationaletects are not considered. 5 the corner and side wells till Ibreakthrough at the side Referring to FIG. 1, there is disclosed four units of wells; (c) and then with these latter wells shut in, proan inverted 5-spot pattern wherein the corner wells of duction is completed at the corner wells till breakthrough. each pattern unit are producing wells, rwhile the inner Alternatively, production can be completed in steps by central well is used for injection. Throughout the drawinitiating and maintaining production at the interior proings the same symbols will be maintained as follows: 10 duction wells till breakthrough thereat; then shutting in Pc, Ps and P1 represent respectively production wells at these `wells and initiating and maintaining production at the corners, along the sides, and the interior wells; and, the side wells till breakthrough thereat; and then closing a solid circle indicates a production well, a crossed circle these latter wells, and initiating and maintaining producindicates a shut-in well, and an arrowed circle indicates tion at the corner wells till breakthrough thereat to coman injection well. plete the production method.

FIG. 1a illustrates the growth of the cusp in one Another alternative would be to have both the interior quadrant of a unit of an inverted 5-spot pattern, wherein and side wells on production till breakthrough at the the secondary flooding lluid is injected into the central interior wells, then shutting in these wells and continuing well and production is maintained at the corner wells unproduction from the side wells till breakthrough thereat, til breakthrough. Such a procedure will produce a sweepand then shutting them in and thereafter initiating and out of approximately 71%. maintaining production at the corner wells till break- Referring to FIG. 2, there is disclosed a quadrilateral through thereat. In this last alternative, after breakthrough side Well pattern of 12 production wells spaced along the at and shut in of the interior wells, production could be outlines of a quadrilateral and a single central injection continued from the side wells and initiated and mainwell. FIG. 3 discloses a special case of such a pattern with 25 tained from the corner wells until breakthrough at the the addition of 4 interior production wells to define the 17- side wells, after which these wells are closed in and prospot pattern as disclosed in our cited, coassigned case. duction maintained at the corner wells till breakthrough Conversely, the 13-spot pattern can be considered as a thereat. A summary of the actual experimental data is modication of the 17-spot pattern, wherein the interior presented in Table I, showing the increase in sweep-out production (or control) wells have been shut in. from the 71% obtainable from the conventional inverted This 17-spot pattern is formed by drilling a single in- 5spot pattern to over 90% by using other patterns with jection well in a center of a 4 x 4 well square, with the the steps described above. advantage of requiring the drilling of one injection well In addition to the type of well pattern, the table inper 9 production wells. In the 17-spot pattern, there are cludes: four corner production wells, 2 producing side wells on 35 (a) Position of interior well (when used), as the fraceach side of the 4 x 4 well square, and four interior protion of the distance from injection well to corner well in duction wells located on the diagonals of the lpattern and a pattern unit', positioned between the central injection well and the (b) Rate distribuiton, given as the ratio of total fluid corner production wells. It is not necessary that the producproduction of each producing well to that of each control tion well be positioned critically inasmuch as this pattern 40 well in the pattern unit, (Qp:Q); can be used wherever a regular drilling pattern was used (c) percentage of Swput at breakthrough into the in developing a production eld. last production Well;

FIG. 2a illustrates the development of the cusp toward (d) Volume of injected uid produced, in terms of pore the corner production well, retarded by spreading of the volume of any eld using the indicated pattern; and gradients, production being maintained at both the corner (e) A brief description of the production procedure and side production wells until breakthrough at the side Ifor each indicated pattern.

TABLE I Pattern Type and Position of Rate Areal Vol. Inj. Fluid Experiment No. Interior Well Distribution Sweep Produced, In Procedure (QD: Qi) Etiiciency Pore Vol.

5-Spot None Uniform 71 0 All wells producing at QD to BT. 13- and 17-Spot: X-l-A. Produce S & I to BT of I. X-1 1/3 2:1 88 0 {X-i-B. s1 I, produce s to BT.

X-l-C SI S; produce K to BT. X-Z-A. Same as X-1-A. X-2 1/3 1:1 87 0 {X-z-B. Same as X-1-B. X-Z-C. Same as X-l-C. X-B-A. Produce all wells to BT of I. X-3 1/3 1:1 87 0 {X-B-B. Same as X-l-B. X-3-C. Same as X-l-C. X4 1/3 None 88 0 [X4-A. Produce S only, to BT.

. SI S; produce K only, to BT.

N oMENcLA'rURE.-BT=Breakthrough; SI=Shut In; K: Corner Wells; I=Interior Wells; S=Side Wells.

wells for the end of the irst phase and then continuing production at the corner Wells only until breakthrough, for the end of the second phase.

FIG. 2b illustrates the splitting of the cusp by producing at the side wells only till breakthrough thereat, as indicated by the dotted outline for the end of phase 1, and then producing from the corner production wells only till breakthrough for a sweep-out of 88% Since the hydrocarbon has re-invaded the vicinity of the shut-in side wells, additional sweep-out can be obtained by placing the side wells on production to increase the sweep-out to 90%. The unswept areas in FIGS. 2a and 2b are the cross hatched portions within the solid lines.

(a) Percentage of sweep (b) Volume of injection tuid handled (c) Time to achieve the sweep.

For a given total field production rate, it will not be possible generally to obtain an increase in sweep-out without at least a proportionate increase of time, which is to be expected. However, if the extra time involved is disproportionately long, the gain in sweep-out may not be economically worthwhile.

Any pattern and/or rate distribution which retards the development, or the advance, of a cusp towards the production wells will increase the sweep-out of a field. Two principal means of doing this are: (a) pinning down the cusp by locating production wells between the injection source and the outer production wells, and keeping these inner (or control) wells on production after breakthrough, as disclosed in our cited coassigned application; and (b) spreading out the cusp by pulling the front toward side wells until breakthrough thereat before allowing it to proceed toward the corner production wells of a pattern unit.

The spreading out of the cusp is in general a more advantageous procedure. It yields as good or better sweepout with less production of injection uid. Further, a higher rate distribution on corner wells of pattern units generally results in much less over-all production of injection uid, but also in less sweep (although exceptions can be found in more complicated patterns).

The advantages of the method disclosed above are eVident. Fewer injection wells are required, more reservoir iluid is recovered prior to breakthrough of injection fluid, and so more ultimate recovery is obtained, as compared with other methods generally employed in secondary recovery operation.

Although emphasis has been placed in this disclosure on the practice of this invention as directed to a secondary recovery operation, particularly employing water or other similar aqueous uid as the injection fluid or displacement fluid, as indicated hereinabove, the advantages obtainable in the practice of this invention are also realized in primary hydrocarbon production operations wherein the hydrocarbon-bearing formation is under the influence of a water drive or gas drive, or both a water and a gas drive, and also in the instance of a secondary recovery operation wherein a gas, such as natural gas, is employed as the injection uid.

As will be apparent to those skilled in the art in the light of the accompanying disclosure, other changes and alternations are possible in the practice of this invention without departing from the spirit or scope thereof.

We claim:

1. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving an injection well surrounded by production wells located at the vertices and along the sides of a quadrilateral which comprises introducing injection fluid into said formation via said injection well, controlling the advance of said injection fluid toward said production wells located at said vertices by producing through the wells located adjacent thereto and on the sides of said quadrilateral, and producing hydrocarbons from said formation via the production wells defining said quadrilateral until breakthrough of said injection fluid thereat.

2. In the method of producing hydrocarbons as defined in claim 1, initiating the production of hydrocarbons from the production wells defining said quadrilateral concurrently with the wells along said side of said quadrilateral, and ceasing the production of hydrocarbons at the quadrilateral side production wells upon breakthrough of said injection fluid thereat.

3. In the method of producing hydrocarbons as defined in claim 1, initiating and maintaining the producion of hydrocarbons from the quadrilateral side production wells until breakthrough thereat of said injection iluid, and thereafter ceasing production of hydrocarbons thereat and initiating and maintaining production of hydrocarbons from the production wells at the vertices of said quadrilateral until breakthrough of said injection fluid thereat.

4. In the method of producing hydrocarbons as defined in claim 3, upon breakthrough of injection fluid at the production wells at the vertices of said quadrilateral, ceasing said production of hydrocarbons thereat and again producing from said quadrilateral side production wells until breakthrough of injection iluid thereat again.

5. In the method of producing hydrocarbons as defined in claim 3, the production wells along the sides of said quadrilateral being at least two in number.

6. A method of producing hydrocarbons from an underground hydrocarbon-bearing formation involving an injection well surrounded by production wells located at the vertices and along the sides of a quadrilateral, and a plurality of wells defining the vertices of an interior quadrilateral positioned along the diagonals through the production wells at the vertices of said interior quadrilateral and the quadrilateral of surrounding production wells, which comprises introducing injection fluid into said formation via said injection well, producing hydrocarbons from the production wells of said interior quadrilateral and the surrounding quadrilateral side production and vertices production Wells till breakthrough of injection uid thereat.

7. In the method of producing hydrocarbons as defined in claim 6, initiating the production of hydrocarbons from the interior quadrilateral production wells and that of the surrounding quadrilateral side production wells and the surrounding quadrilateral vertices production Wells consecutively following breakthrough of injection uid at the production wells of the interior quadrilateral and the side production wells of the surrounding quadrilateral respectively.

8. In the method of producing hydrocarbons as defined in claim 6, initiating production of hydrocarbons concurrently at the production wells of the interior quadrilateral and of the side Wells of the surrounding quadrilateral until breakthrough of injection fluid at the interior quadrilateral production wells, and thereafter ceasing production thereat while maintaining production at the surrounding quadrilateral side production wells until breakthrough of injection fluid thereat and thereafter ceasing production of hydrocarbons at said quadrilateral side production wells and initiating and maintaining production of hydrocarbons at the quadrilateral vertices production Wells until breakthrough of injection fluid thereat.

9. In the method of producing hydrocarbons as defined in claim 6, initiating production of hydrocarbons concurrently at the production wells of the interior quadrilateral and of the surrounding quadrilateral until breakthrough of injection fluid at the interior quadrilateral production wells and thereafter ceasing production thereat while maintaining production at the surrounding quadrilateral side production wells and vertices production wells until breakthrough of injection fiuid at said quadrilateral side production wells, and thereafter ceasing production of hydrocarbons thereat and maintaining production of hydrocarbons at the quadrilateral vertices production wells until lbreakthrough of injection fluid thereat.

10. In the method of producing hydrocarbons as defined in claim 6, the production wells along the sides of the surrounding quadrilateral being at least two in number.

References Cited UNITED STATES PATENTS 2,885,002 5/1959 Jenks 166--9 3,113,618 12/1963 Oakes 166-9 3,199,587 8/ 1965 Santourian 166-9 3,205,943 9/ 1965 Foulks 166-9 3,270,809 9/1966 Connally 166-9 3,286,768 11/ 1966 Heller 166-9 3,332,480 7/1967 Parrish 166-11 X NILE C. BYERS, IR., Primary Examiner. 

